In my earlier U.S. Pat. No. 3,686,864, I disclosed a braking system having a master cylinder which incorporates a warning failure switch, a proportioning valve and a metering valve. Through this master cylinder it is possible to achieve simultaneous actuation of disc brakes on the front wheels of a vehicle and drum brakes on the rear wheels of a vehicle. To bypass the proportioning valve, a shuttle valve is required to move a first lever which in turn moves a second lever. The second lever opens a poppet to allow the entire hydraulic fluid force developed by a second piston to be communicated to the rear wheels whenever a malfunction occurs in the front braking system. This type of lever actuation system, while functionally adequate for engineering laboratory testing, has not been successfully adapted to production manufacturing.